Not sure if it the 'right' way but if you use one that has the little ball knob on it put that towards the fabric as it helps eliminate accidentally ripping your fabric while you are ripping the threads.
I also use mine like a knife instead of under each stitch I just cut several threads at once. I used to use a scalpel as I had a few disposable ones. But after 30 years they finally got dull and I can't get anymore.
And then there is also if you just rip a few stitches out here and there along the seam you are taking out, you can pull the threads and have a longer piece of thread instead of a bunch of little ones.
And then...... next ----- how does everyone else use there's?